1. Field of the Invention
The present invention generally relates to gas lasers and, more particularly, to a new tube structure for a mirrorless gas laser.
2. Description of the Prior Art
In a conventional waveguide gas laser, a capillary tube with a hollow opening through which a laser active gas is made to propagate at high pressure is used. End mirrors are employed to reflect the energy back and forth through the opening to achieve the desired amplification and the lasing action. As is known, these mirrors reduce the overall gain and increase the laser complexity and maintenance since the mirrors have to be aligned very precisely, and are subject to damage, requiring periodic replacement.
In recent years, mirrorless distributed feedback lasers have been proposed and described in the literature. In such lasers, distributed feedback, which eliminates the need for the mirrors, is achieved by providing a periodically corrugated surface along the length of the amplifying medium. Distributed feedback is achieved when the corrugation periodicity is a function of the desired wavelength of emission.
In a recent article by Dietrich Marcuse, entitled "Hollow Dielectric Waveguides for Distributed Feedback Lasers", IEEE Journal of Quantum Electronics, Volume QE-8 No. 7, July 1972, page 661, the performance of a dielectric capillary tube with a hollow opening that fulfills the dual role of a guidance structure for the gas laser and provides distributed feedback so as to eliminate the need for the external mirrors is analyzed. The feedback is achieved by means of periodic ripples or corrugation of the inner surface of the hollow opening of the tube. In the article it is recognized that some waves propagating in the tube opening will strike the tube inner surface. Since the tube has a higher index of refraction than that in the opening (which can be assumed to be equal to one), some of the energy of the waves striking the opening inner surface will be transmitted through the tube wall, resulting in lower efficiency which is most undesirable. However, in the article based on theoretical analysis, it is contended that despite these losses the tube with the corrugated opening which produces the distributed feedback is still more efficient than the conventional tube requiring the use of external mirrors.